How to Stop 12-Volt Sprayer Pump From Pulsing, Surging, & Cycling On/Off

I used to get frustrated when my ATV sprayer would pulsate and surge. The flow out of the spray gun was inconsistent and it was hard to get the pump to run smoothly. So I decided to do some research and find out exactly what causes 12-volt sprayers to pulse.

Sprayers pulse because the 12-volt pumps they use are equipped with pressure switches that shut off the pump when a certain pressure is reached. When the pressure drops the pump will start again. This results in inconsistent flow or pulsing/surging. This not only limits the effectiveness of a sprayer but can wear out the motor, and the demand switch. Fortunately, fixing this issue is not complicated. Let’s look into how this happens and what to do about it.

What is Sprayer Pulsing/Surging?

Pulsing and surging is when the sprayer output is inconsistent due to the pump cycling on/off. The result is a surging or pulsing flow coming out of your sprayer gun or nozzles. You will notice the sound of the motor changing as it starts and stops. If you have a pressure gauge, you will see the needle in the gauge bouncing up and down.

Why Does My Sprayer Pulse/Surge Video

What Causes Pulsation?

If your pump is cycling on and off it will cause pulsing or surging. The cycling happens because the pumps have a “demand” switch. The demand switch is set to shut the pump off at a certain pressure. For example, the Chapin 97300E 15 Gallon sprayer has a 12-volt pump with a pressure or “demand” switch that will shut the pump off at 60 PSI.

Once the pump is off, the pressure in your system will drop and the pump will turn on again. If nothing about the discharge plumbing is changed, the pump will continue to cycle on and off. There are many reasons that can cause this to happen.

Are You Using Too Long of A Sprayer Hose?

Long lengths of discharge hose can lead to sprayer pulsing. Every foot of hose you add will increase the amount of pressure loss. So your sprayer operating pressure will increase as the pump works to overcome this resistance. If this extra resistance adds up to enough pressure it can activate the pressure switch and then your sprayer will start to surge.

Is Your Sprayer Nozzle Too Small?

Most spray nozzles on ATV or spot sprayers are small. They may only allow 0.10 – 1 GPM. The pumps used on these sprayers will put out anywhere from 1-5 GPM. The restriction from the nozzle will result in pressure build-up and your pump will start surging.

There are many nozzles available. Each different type (solid stream, flat fan, adjustable, etc) will come in various sizes or flow rates. Flow rate is measured in GPM (gallons per minute). You can refer to your sprayer or spray gun manual to see what size nozzle(s) they provide with the sprayer.

Is Your Sprayer Pump Too Large?

Many people will purchase a pump that is larger than necessary. 12-volt sprayer pumps are available with flow rates of about 1-5 gallons per minute. The cost of the larger flow pumps is usually not much more than the smaller flow rates. This leads people to go with the larger pump, but their sprayer is not set up to handle that much flow.

A 5 GPM pump with a ¼ inch or ⅜ inch discharge hose and a 0.3 GPM spray tip will cause the sprayer to pulsate. There is simply too much restriction in the discharge line to handle the flow of that pump.

Discharge Hose Blockage

If you have operated your sprayer just fine through multiple seasons, then all of a sudden it begins to surge, you could have a plug in the discharge line. This could come from chemical residue buildup or foreign debris getting in the sprayer. Flushing the sprayer with a tank cleaner can help remove chemical and pesticide residue.

Why Do 12 Volt Sprayer Pumps Have a Pressure Switch? 

12-volt sprayer pumps are available with or without a pressure/demand switch. The demand-style pumps are often used with applications using a trigger gun. The pump starts when the trigger on your spray wand or gun is pulled. When you let go of the trigger the pump shuts off. So the pump only runs “on-demand”.

Does Pulsation Hurt My Sprayer?

A sprayer that is pulsing or surging will not only limit the effectiveness of your sprayer but can also wear out your sprayer components.

Pressure Switch

The pressure switch contains an electric relay. While the surging of the sprayer itself doesn’t affect the switch relay, the cycling on and off does. The contactors on the switch relay have a life span. Each time the switch is activated it reduces the life span of the contactors. Eventually, they will fail. With a bad pressure switch on your pump, it will not run.

Pressure Gauge

Pressure gauges are made up of mechanical metal components. These components can wear out over time, especially when the pressure is jumping up and down quickly. The gauge may become “uncalibrated” and need to be replaced. Liquid-filled gauges can help reduce the wear on the gauge components but it is best to eliminate the pulsing in your sprayer.

How to Fix Pulsation?

The first thing to check is whether or not your sprayer has a pressure-regulating valve. A regulating valve provides you with the ability to control your operating pressure. Adjusting the knob on the regulating valve increases or decreases the amount of water being bypassed back to the sprayer tank. So, in most cases, you can eliminate the pulsing in your sprayer.

For Sprayers With a Regulating Valve

When you start your sprayer and it begins to cycle on and off, you will simply adjust the control knob on the regulating valve until the pump stops surging. If your sprayer is equipped with a pressure gauge you will see the needle begin to stabilize and then rest on a specific pressure when the sprayer stops pulsing. Once the regulating valve is set you should be able to turn your sprayer on or off without any pulsing or surging.

If adjusting your regulating valve does not completely eliminate the surging, then you still need to have another issue. Likely, you will find that either your hose is too long, the inside diameter of your hose is too small, the spray nozzle is too small, or there could be a plug in the discharge line.

For Sprayers Without A Regulating Valve

If your sprayer does not have a regulating valve, the first recommendation would be to add one! With no regulating valve, you have very little control over the operating pressure. When the flow from your sprayer gun or boom starts to pulse, there isn’t much you can do to stop it.

You can check all your nozzles for blocks, shorten the hose length, or switch to a hose with a large inside diameter. But in the end, the regulating valve will give you the control you need to dial in your sprayer and allow the pump to operate smoothly.

A regulating valve will also make your sprayer more effective because the flow that is bypassed will help agitate your spray solution. This can ensure that your chemical or pesticide is being applied evenly, giving it the best chance to do what you want: eliminate pests or weeds.

Things to Keep In Mind When Using a 12-Volt Sprayer

Most 12-volt sprayers are very similar, but the specifics of the sprayers will differ. Pump flow rate, pressure, spray nozzle size, etc. will affect your sprayer’s performance. Knowing the details of your pump will help you avoid issues when making a change to your sprayer like adding a boom or longer hose.

Adding a regulating valve can also help you to ensure your sprayer will operate smoothly even if you replace your pump or change the spray boom or sprayer nozzle. Follow these guidelines and you can save time and money by prolonging the life of your sprayer pump.

Shane Blomendahl

I have more than a decade of experience using, building, studying, and testing sprayers in several applications. With the knowledge I have gained I want to provide straight forward and detailed answers for DIY homeowners, farmers, and commercial turf and tree care pros.

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